Aircraft are exposed to a variety of temperature conditions during flight and while out of service on the ground. Fuel, when tanked in areas directly adjoining exterior surfaces of the aircraft may change the temperature of those surfaces without warning. In the event the surface temperature or the aircraft falls below 32.degree. F. and there is mist, rain or high humidity in the ambient air; ice can form in thin films on these surfaces. If undetected, this ice can dislodge during operation of the aircraft and fly into other portions of the aircraft especially into engine parts, causing damage that may affect the performance of the aircraft and if severe, can completely stop engine operation. Aircraft which have wing fuel tanks with jet engines mounted behind the wings are especially prone to what is termed "ICE FOD" or "ice foreign object engine damage". In addition, aircraft taxiing behind aircraft with ice build-up may be exposed to showers of ice as the former aircraft begins take-off. In addition, sensors and control surfaces may become fouled with ice resulting in inaccurate readings and unreliable control during flight.
The magnitude of the problem was reported by the U.S. Department of Transportation Federal Aviation Administration in General Aviation Airworthiness Alert Special Issue AC No. 43-16. In this report, 516 known ice related accidents occurred from April 1976 to April 1987 with 567 fatalities. In this report certain aircraft were found to be more prone to ice formation than others. The recommendation of the report is as follows: